M. Wiedmann et al., RIBOTYPES AND VIRULENCE GENE POLYMORPHISMS SUGGEST 3 DISTINCT LISTERIA-MONOCYTOGENES LINEAGES WITH DIFFERENCES IN PATHOGENIC POTENTIAL, Infection and immunity, 65(7), 1997, pp. 2707-2716
A total of 133 Listeria monocytogenes isolates were characterized by r
ibotyping and allelic analysis of the virulence genes hly, actA, and i
nlA to uncover linkages between independent phylogenetic and specific
virulence markers. PCR-restriction fragment length polymorphisms revea
led 8 hly, 11 inlA, and 2 actA alleles. The combination of these virul
ence gene alleles and ribotype patterns separated L. monocytogenes int
o three distinct lineages. While distinct hly and inlA alleles were ge
nerally found to cluster into these three lineages, actA alleles segre
gated independently. These three phylogenetic lineages were confirmed
when 22 partial actA DNA sequences were analyzed. The clinical history
of the L. monocytogenes strains showed evidence for differences in pa
thogenic potential among the three lineages. Lineage I contains all st
rains isolated during epidemic outbreaks of listeriosis, while no huma
n isolates were found in lineage III. Animal isolates were found in al
l three lineages. We found evidence that isolates from lineages I and
In have a higher plaquing efficiency than lineage II strains in a cell
culture assay. Strains from lineage III also seem to form larger plaq
ues than strains from lineage II. A distinctive ribotype fragment and
unique 16S rRNA gene sequences furthermore suggest that lineage III mi
ght represent a L. monocytogenes subspecies. None of the 20 human isol
ates available but 11% of our animal isolates were grouped in this lin
eage, indicating that strains in this lineage might have reduced virul
ence for humans.